Aluminium Curtain Wall vs ACP Cladding

A curtain wall is a glazed non-structural envelope hung on the building frame, ACP is a panel cladding, and a ventilated facade is a rainscreen with an air gap. Choose by structure, glazing share, fire rules and thermal targets, and always request shop drawings and test reports before committing to a system.

Which facade system suits which building?

The three systems solve different problems. A curtain wall is the right answer when the facade is mostly glass and the building wants a continuous, glazed envelope with sightlines maintained across floors. ACP cladding suits projects that need a solid, coloured or metallic panel finish with fast installation and a lower material cost per square metre. A ventilated facade — whether in metal, ceramic, fibre cement or stone — suits buildings that want a rainscreen with a drained air cavity behind it, which manages moisture and improves thermal behaviour. Send the elevations, the fire requirements and the thermal target and we will quote the system that fits, with shop drawings and test reports named: request a quote.

The decision is structural before it is aesthetic. A curtain wall hangs from the slab edge and carries only its own weight and wind load; the building frame carries the rest. A ventilated facade is fixed back to the structure through a subframe, and the subframe must be designed for the panel weight and the wind suction. ACP can be installed as a rainscreen too, but its fire behaviour depends on the core, and that question must be answered before the system is chosen.

Comparison of facade systems

The table below is qualitative. It reflects how the systems are positioned in architectural practice; it is not a performance ranking for any specific product.

Curtain wall: stick versus unitised

A stick curtain wall is assembled on site from vertical mullions and horizontal transoms, with glass or spandrel panels installed afterwards. It is flexible for changes and needs less factory work, but it demands more site labour and longer access equipment hire. A unitised curtain wall is fabricated in factory-sized modules, glazed in the workshop, and hung on the building as complete panels. It is faster on site and more consistent in quality, but it needs precise survey, heavy lifting and early design freeze.

The choice between them is a programme and logistics decision. A tower with repetitive floors favours unitised; a building with complex geometry or late design changes favours stick. The buyer should ask the facade contractor which system it proposes and why, and should confirm that the proposed system matches the building's geometry and the site's lifting capacity.

ACP and composite cladding: fire questions

Aluminium composite panels consist of two aluminium skins bonded to a core. The core may be polyethylene, a fire-retardant mineral core, or a combination, and the core determines the fire behaviour. National regulations classify the panels differently; some markets restrict their use on buildings above certain heights, and others require a specific core type for public buildings.

The buyer must ask for the core type, the reaction-to-fire classification and the test report behind it. A panel described as "fire-rated" without a test report and a classification is not a specification. The buyer should also ask how the panel behaves in a cavity — the ventilated facade behind an ACP panel changes the fire dynamics, and the system, not just the panel, must be considered.

Ventilated facade: the rainscreen principle

A ventilated facade consists of an outer cladding panel, an air cavity, and an insulation layer fixed to the structure. The cavity is open at the top and bottom, or at each floor, so that air rises through it and carries moisture out. The outer panel sheds most of the rain; the cavity drains what penetrates, and the insulation stays dry.

The system works with many materials: aluminium, zinc, copper, fibre cement, ceramic, HPL and natural stone. The buyer chooses the material by appearance, durability and cost, and the subframe by the panel's weight and the building's movement. The key detail is the cavity depth and the ventilation openings: too shallow or too blocked, and the rainscreen stops working as designed.

Glass and thermal performance

For curtain walls, the thermal performance is a glazing question. The U-value of the vision area, the solar heat gain coefficient and the light transmittance are specified together, because improving one often worsens another. A low-E coating reduces heat gain but may reduce light; a reflective coating controls glare but affects the facade's appearance. The buyer should ask for the glazing specification as a package, not as a list of properties.

For ACP and ventilated facades, the thermal performance comes from the insulation behind the panel. The insulation thickness is set by the building's energy code, and the subframe must accommodate it without creating thermal bridges. The buyer should ask the facade contractor for the calculated U-value of the complete assembly — panel, cavity, insulation and subframe — not just the insulation's laboratory value.

Procurement and shop drawings

The procurement process for a facade system follows a standard sequence, and the buyer should insist on each step. The table below shows the stages and the documents that belong to each.

The shop drawings are the core document. They show every panel, every anchor, every joint and every interface with the structure, the windows and the roof. The buyer reviews them before fabrication begins, because changes after fabrication are expensive and slow.

Thermal bridging and condensation risk

Every facade system has thermal bridges: the mullions of a curtain wall, the subframe of a ventilated facade, the fixings that penetrate the insulation. A thermal bridge is a path where heat flows more easily than through the surrounding construction, and it shows up first as condensation on the inside surface in cold weather, or as a local cold spot that feels like a draft.

The buyer should ask the facade contractor for the linear thermal transmittance of the principal bridges — the mullion, the transom, the anchor — and for the condensation risk analysis of the worst detail. A system that looks fine on a thermal image of the field can still fail at the slab edge, the window jamb or the parapet, where the insulation is interrupted and the bridge is longest.

The practical mitigations are standard: thermal breaks in aluminium profiles, insulation that continues past the slab edge, and anchors that are isolated from the inside surface with low-conductivity pads. The buyer does not design these details, but the buyer should confirm that the contractor has calculated them, because a facade that condensates is a facade that will be replaced.

Movement, tolerances and interfaces

A building moves. It sways in the wind, it grows and shrinks with temperature, and it settles over time. A facade system must absorb that movement without cracking, leaking or transferring load to the glazing. The curtain wall's stack joints, the ventilated facade's panel joints and the ACP's expansion joints are all movement details, and they are the first places a facade fails.

The buyer should ask how each system handles movement at each floor, at each corner, and at the interface with the roof and the podium. The answer should be in the shop drawings, not in a verbal assurance. The buyer should also confirm that the survey before fabrication is accurate, because a unitised curtain wall built to a survey that is out by twenty millimetres will not fit on the slab edge.

Maintenance and access planning

A facade that cannot be maintained is a facade that will deteriorate. The buyer should ask how each system is cleaned, how the panels are replaced if one is damaged, and how the ventilated cavity is inspected. A curtain wall needs a building maintenance unit or a cradle system; an ACP facade may need access to the cavity for inspection; a ventilated facade needs the cavity kept clear of debris.

The maintenance plan is part of the procurement, not an afterthought. The buyer should ask the contractor for the recommended maintenance interval, the access method and the replacement strategy for a damaged panel, and should confirm that the building's design accommodates the access equipment. A facade that is designed without maintenance in mind is a facade that will be cleaned poorly and replaced expensively.

Acoustic performance of facade systems

A facade is also an acoustic barrier. Traffic noise, aircraft, and neighbouring machinery all arrive at the outside face and pass through the system at different rates depending on the material, the joints and the glazing. The curtain wall's acoustic performance is dominated by the glass: a laminated unit with a sound-dampening interlayer outperforms a monolithic pane of the same thickness. The ACP panel's performance is dominated by the panel itself and the insulation behind it; a thin metal skin over a cavity transmits more sound than a solid panel of the same area.

The buyer should ask the acoustic consultant for the required sound reduction for each facade orientation, and then ask the contractor for the tested or calculated performance of the proposed assembly. A rating measured on a laboratory sample applies to the system, not to a field assembly with open joints and gaps, so the buyer should confirm that the joints and the perimeter seals are included in the acoustic specification.

Sustainability and end-of-life considerations

A facade system's environmental profile spans its production, its service life and its disposal. Aluminium is recyclable, and both curtain wall profiles and ACP skins can be recovered at end of life, though the composite panel's core complicates the recycling path. Stone and ceramic rainscreen panels are inert and durable but heavy, which increases the transport energy. The buyer should ask the maker for the recycled content of the aluminium, the expected service life of the coating or finish, and the disassembly strategy — how the panels come off the building and where they go afterwards.

The practical questions are simple. Can the panels be separated by material type at demolition? Is the coating durable enough that the facade does not need recoating inside the building's planned life? Does the maker take back the packaging and the offcuts? A facade that is designed for disassembly is cheaper to maintain and less wasteful at the end of its life.

Frequently Asked Questions

Curtain wall or ACP for an office building?

It depends on the glazing share and the budget. An office building with a glass-dominant facade and a continuous appearance favours a curtain wall; a building with punch windows and a panelised facade favours ACP. The structural and fire questions must be answered for either choice.

What is unitised glazing?

Unitised glazing is curtain wall fabricated as complete modules in the factory, with glass already installed. The modules are lifted into place and connected to the building and to each other. It is faster and more consistent than stick-built curtain wall, but it needs precise survey and heavy lifting.

How do I check ACP fire behaviour?

Ask for the core type, the reaction-to-fire classification and the test report behind it. Confirm that the classification applies to the panel thickness and the core being ordered, and check the national regulation for the building's height and use. A general claim of fire resistance is not a specification.

Can marble be used on a ventilated facade?

Yes. Natural stone — including marble — can be used as a rainscreen panel on a ventilated facade, fixed with mechanical anchors to a subframe. The stone thickness, the fixing method and the anchor layout are engineered for the specific stone and the building's wind loads. See Marble wall cladding for the material side.

Who designs the anchors?

The anchor and subframe design is the facade contractor's responsibility, working with the structural engineer. The buyer should confirm that the anchor layout is drawn, calculated and approved before fabrication begins, and that the anchors are installed to the drawn positions during construction.

What drawings do I need to start a facade project?

At minimum: elevation drawings showing the facade extent and material zones, the structural drawings showing the slab edges and the loads, and the architectural drawings showing the window and door openings. The facade contractor develops these into shop drawings, but the buyer must provide the starting set.

Sources and standards

• EN 13501-1 — Fire classification of construction products and building elements. https://www.cencenelec.eu
• EN 13830 — Curtain walling — product standard. https://www.cencenelec.eu
• National regulations govern the use of composite panels; ask the maker for the applicable classification.

To compare the three systems on your own drawings, contact us or call +90 505 679 78 03.